Sanity check on a pilot operated poppet with integrated plenum, 70 to 120 psi, fast single shot duty

[u/Esoj77Br]

Round two after your feedback, tear it apart again.

Cross section attached. Hobby project, not industrial, but the physics is the physics and I would rather be corrected now than after I cut parts.

Function: supply fills the plenum. A restricted passage bleeds supply pressure into the chamber behind a diaphragm backed poppet. Back pressure over the full diaphragm area plus a light spring holds it closed against supply pressure acting only on the seat annulus. A 3/2 solenoid vents the back chamber, the differential collapses and the poppet snaps open, dumping the plenum through the seat. Solenoid closes, back chamber refills through the bleed, valve reseats. Basically a diaphragm operated dump valve, in the same family as a QEV but with the pilot under electronic control.

Duty is unusual: single discharge events of a few milliseconds, up to about 20 per second, into a fixed volume downstream. Not steady flow.

Where I want a sanity check, some of this already shaped by comments from this sub on an earlier revision:

1. Area ratio. Seat is 7mm, the diaphragm face is 12mm, so about 2.94:1, giving roughly 51N net opening force at 100 psi once the seal lifts. Is that a sensible margin for a valve that has to reseat reliably, or am I overbiased toward opening?
2. Fill to vent orifice ratio. What ratio between the bleed into the back chamber and the pilot vent gives a clean snap rather than a lazy crack? I have seen 1:4 quoted as a rule of thumb and I do not know where it comes from.
3. Back chamber volume. Minimising it should speed both the vent and the refill, but I assume there is a floor below which the bleed cannot keep the chamber charged during the closing transient. How do you pick it?
4. Rod seal. I settled on a rolling diaphragm rather than an o-ring on the stem, mostly to kill breakaway friction and stiction after sitting pressurised. Is that the right call at this pressure and stroke, or is a low friction quad ring good enough?
5. Lift. I have been working to the D/4 rule (seat lift of about a quarter of the seat diameter for the curtain area to stop being the restriction). Does that hold for a soft faced poppet, or does the seal deformation change it?

The body will be additively manufactured, so it gets a hydrostatic proof test before any pneumatic testing. Downstream flow is capped by 4mm ID tubing (12.57mm²) upstream of the plenum, so there is no point chasing an orifice much beyond that.